A progress in an electronic display as man machine interface has resulted in popularization of an interactive input system. Among others, an apparatus in which a touch panel (a digitizer) is united with a display screen is widely used in various fields such as an ATM (automated teller machine), a merchandise management, an outworking (canvassing, selling), a guide sign, and an entertainment device. Since use of the touch panel in combination with a lightweight and thin display (e.g., a liquid crystal display) dispenses with any keyboard and exhibits the features of the display, the touch panel is increasingly used for mobile devices. The touch panel (or touch screen) is a device for inputting (or feeding) information or instructions to a computer by touching a prescribed area on the touch panel with an input means or device, such as a finger or a pen (a digital pen or a stylus). According to the position detection method, the touch panel can be classified into an optical system, an ultrasonic-wave system, a capacitive system, a resistive system, and other systems. Among these systems, the capacitive system detects the location of the touch using a change in capacitance. In light of excellent functionality, a projected capacitive touch panel of ITO grid system, which is now being used for mobile devices, is receiving a lot of attention. The mobile devices include a smartphone, a mobile phone, an electronic paper, a tablet personal computer (PC), a pen tablet (or a graphics tablet), and a game console. Among the capacitive touch panels, a pen-input touch panel, which uses a pen as an input device, is also now being widely used and being increasingly applied for a smartphone, an electronic paper, a tablet PC, a pen tablet, a game console, and a PC. The display of the touch panel (or touch screen) is provided with, on a surface thereof, a hardcoat film, an anti-Newton-ring film, a soft film, or other films according to purposes.
As the pen-input touch panel is widely used for various purposes, the touchpanel requires higher functions for enabling smooth or excellent writing in pen input, e.g., for enabling smooth or excellent writing similar to writing on paper with a pencil. Unfortunately, a touch panel provided with the soft film, which has an excessively strong resistance, never enables smooth writing similar to writing on paper with a pencil.
Meanwhile, for the hardcoat film or the anti-Newton-ring film, there has been reported a method for forming an uneven structure on a surface of the film to improve the finger touch (feel) of the film. Japanese Patent Application Laid-Open Publication No. 2010-153298 (JP-2010-153298A, Patent Document 1) discloses a laminated film for a touch panel, the laminated film comprising, in sequence, a hardcoat layer, a substrate consisting of a polyester film, and a transparent conductive layer consisting of a metal oxide. The hardcoat layer has an average area surface roughness of 0.08 to 0.30 μm, an average friction coefficient MIU of KES surface friction characteristic value of 0.13 to 0.17, and a fluctuation MMD of friction coefficient of 0.006 to 0.015. This document discloses a hardcoat liquid containing an acrylic hardcoat liquid and an inorganic or organic particle having an average particle size of 2 to 7 μm. Moreover, the document discloses that the ratio of the inorganic or organic particle is 0.5 to 20 parts by weight relative to 100 parts by weight of a cured resin and that the inorganic or organic particle preferably includes a porous silica-series fine particle having a pore volume of not smaller than 1.7 ml/g in light of transparency.
Since the hardcoat layer is formed from the fine particle and the crosslinkable polymer, the film has an improved finger touch to some degree. Unfortunately, for pen-input operation, a digital pen excessively slides on the film. In particular, the writing smoothness is irregular during pen-input operation (or the writing smoothness (or the feeling of writing) is not constant between the beginning and the midst of pen-input operation). Thus the film never enables smooth writing similar to writing on paper with a pencil.